1. Field of the Invention
The present invention relates to electrophotographic (EP) printers, and, more particularly, to such printers capable of and a method for changing fuser member speed and/or substrate transport assembly speed in order to minimize print defects caused by speed mismatches between the fuser member and the substrate transport assembly.
2. Description of the Related Art
Cost and market pressures promote the design of the smallest possible printer with the shortest possible length of substrate path. Short substrate paths mean that most substrates are involved in more than one operation at once. For example, a substrate in a printer may be at one or more imaging stations while it is also located in a fuser assembly.
Tandem color laser printers may use a substrate transport belt to move a substrate past successive imaging stations before fusing the final image onto the substrate. If a substrate is pulled taut between an imaging nip and a nip in the fuser assembly, a disturbance force transmitted via the substrate from the fuser assembly to the imaging nip defined by a photoconductive drum and the substrate transport belt may cause image registration or alignment errors. To prevent such errors, the fuser assembly may be under driven so that a substrate bubble accumulates between the transport belt and the fuser assembly. Since the fuser assembly runs more slowly, a substrate never becomes taut, so less disturbance force can be transmitted from the fuser assembly to the imaging nip. However, the pursuit of small machines means that substrate bubbles must be constrained to stay as small as possible. If a machine is designed for a certain maximum bubble size, large velocity variations can make the substrate form a bigger bubble. If this happens, the substrate may make contact structure within the printer which may scrape across the image area, causing print defects.
There is a need for driving the fuser assembly so that an outer surface speed of a rotating fuser member is less than the speed of the substrate transport assembly upstream from it such that a substrate bubble develops between the fuser assembly and the substrate transport assembly, yet, in the case of long substrates or envelopes, the bubble is not allowed to grow too large as to result in print defects.